Z-scheme Heterostructure Research Articles

Engineering a Z-Scheme Heterostructure on ZnIn2S4@NH2-MIL-125 Composites for Boosting the Photocatalytic Performance.

Constructing a Z-scheme heterostructure on a metal-organic framework (MOF) composite with an explicit charge transfer mechanism at the interface is considered to be an effective strategy for improving the photocatalytic performance of MOFs. Herein, an internal electric field (IEF)-induced Z-scheme heterostructure on the ZnIn2S4@NH2-MIL-125 composite is designed and fabricated by a facile electrostatic self-assembly process. Systematic investigations reveal that close interfacial contact and difference in work function between NH2-MIL-125 and ZnIn2S4 enable the formation of the IEF, which drives the Z-scheme charge transfer as revealed by the in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), photoirradiated Kelvin probe force microscope (KPFM) measurement, electron paramagnetic resonance (EPR) radical trapping experiment, as well as density functional theory (DFT) calculation; meanwhile, directions of the interfacial IEFs are determined. Benefiting from the unique merit of IEF-induced Z-scheme charge transfer, the optimized ZnIn2S4@NH2-MIL-125 composite exhibits significantly enhanced photocatalytic activity for the photoreduction of 4-nitroaniline (4-NA) to p-phenylenediamine (PPD) under visible light irradiation. This work not only provides in-depth insights for charge transfer in the IEF-induced Z scheme heterostructure but also affords useful inspirations on designing the Z-scheme MOF composite to boost the photocatalytic performance.

A direct Z-scheme BS/PtO2 van der Waals heterojunction for enhanced visible-light photocatalytic water splitting: a first-principles study.

A direct Z-scheme heterostructure holds a unique advantage in solar-driven overall water splitting, while the rational design of efficient photocatalysts for water splitting in such heterostructures remains a challenge. Based on first-principles calculations, this study proposes a novel direct Z-scheme two-dimensional (2D) van der Waals (vdW) heterostructure photocatalyst, denoted as BS/PtO2. Its band edges match the oxidation-reduction potentials of water, satisfying the conditions for the oxidation and reduction of water. Under acidic conditions (pH = 0), the results of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) indicate that BS/PtO2 can drive the OER without the need for an external bias, while the HER requires catalytic assistance. Interestingly, compared to single-layer materials, this heterostructure exhibits a significant enhancement in visible light absorption, implying a more efficient solar energy conversion capability. Therefore, the BS/PtO2 heterostructure holds the potential to become a promising direct Z-scheme photocatalyst with efficient visible light activity.

Bioinspired notched volvox-like nested Z-scheme heterostructure improves solar-energy utilization for high visible-light-driven hydrogen production

Bioinspired by the nested structure of volvox with multi-subcell, a facile and universal symbiosis hydrothermal strategy is reported to synthesize volvox-like double-core nested hollow materials for efficient visible-light-driven hydrogen production.

Augmented photocatalysis induced by 1T-MoS2 bridged 2D/2D MgIn2S4@1T/2H-MoS2 Z-scheme heterojunction: mechanistic insights into H2O2 and H2 evolution.

In the realm of composite photocatalysts, the fusion of the co-catalyst effect with interfacial engineering is recognized as a potent strategy for facilitating the segregation and migration of photo-induced charge carriers. Herein, an innovative mediator-based Z-scheme hybrid, i.e. MIS@1T/2H-MoS2, has been well designed by pairing MIS with 1T/2H-MoS2via a facile hydrothermal strategy as a competent photocatalyst for H2O2 and H2 generation. The co-catalyst, i.e. metallic 1T-phase bridging between semiconducting 2H-MoS2 and MIS, serves as a solid state electron mediator in the heterostructure. Morphological findings revealed the growth of 1T/2H-MoS2 nanoflowers over MIS microflowers, verifying the close interaction between MIS and 1T/2H-MoS2. By virtue of accelerated e-/h+ pair separation and migration efficiency along with a proliferated density of active sites, the MMoS2-30 photocatalyst yields an optimum H2O2 of 35 μmol h-1 and H2 of 370 μmol h-1 (ACE of 5.9%), which is 3 and 2.7 fold higher than pristine MIS. This obvious enhancement can be attributed to photoluminescence and electrochemical aspects that substantiate the diminished charge transfer resistance along with improved charge carrier separation, representing a good example of a noble metal-free photocatalyst. The proposed Z-scheme charge transfer mechanism is aided by time-resolved photoluminescence (TRPL), XPS, radical trapping experiments, and EPR analysis. Overall, this endeavour provides advanced insights into the architecture of noble metal-free Z-scheme heterostructures, offering promising prospects in photocatalytic applications.

Zr-based metal–organic framework PCN-222@defective ZnIn2S4 core–shell Z-scheme heterojunctions toward efficient charge separation and optimized photocatalytic performance

PCN-222@VIn-ZnIn2S4 core–shell Z-scheme heterostructure containing indium defects is fabricated via solvothermal method, and it shows excellent photocatalytic degradation of tetracycline and hydrolytic hydrogen production.

Ultrafast carrier recombination in a BC6N/SnXY Z-scheme heterostructure for water splitting: insights from ground- and excited-state carrier dynamics

This study shows BC6N/SnSe2 as a Z-type heterostructure with ultrafast interlayer recombination, exhibiting enhanced OER reactivity in aqueous environments using the implicit solvent model.

Construction of visible light responsive GO-stimulated In2O3/BiVO4 Z-scheme heterostructure: Photocatalytic degradation of dye & antibiotics, anticancer activity and toxicity elimination

A ternary nanocomposite, In2O3/GO/BiVO4, was created using the hydrothermal process, establishing a heterojunction between In2O3 and BiVO4 with the addition of graphene oxide nanosheets. The synthesized materials underwent characterization using various standard analytical techniques, including diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), electron spin resonance spectroscopy (ESR), energy-dispersive X-ray (EDX), and transmission electron microscopy (TEM). The developed materials showed notable efficacy in degrading MB dye and antibiotics such as ciprofloxacin and tetracycline, when exposed to visible light in an aqueous suspension. The photocatalyst, 10 wt% In2O3/GO/BiVO4 (10IBG) showed better activity compared with the pure and other composite materials. The enhanced activity could be attributed to the synergistic effects of charge carrier separation and electron mediation facilitated by graphene oxide via Z-scheme pathway. The successful integration of graphene oxide in the heterostructure underscores its potential as a promising strategy for developing high-performance photocatalysts for the elimination of organic pollutants. Furthermore, the mechanism investigation underlying photocatalytic degradation of organic pollutants using the 10IBG heterostructure photocatalyst is conducted through trapping experiments, which indicates that the degradation is primarily contributedby superoxide radical anions (O2•-) and hydroxyl radicals (•OH). Moreover, 10IBG photocatalyst displayed remarkable anticancer activity against A549 lung cancer cell lines, whereas the cell viability was reduced from 18% in the dark medium to 58% when exposed to visible light. In terms of toxicity assessment, the 10IBG heterostructure photocatalyst demonstrated quick eradication of antibiotic toxicity and established itself as a promising and cost-effective photocatalyst for wastewater treatment.

Direct Z-scheme In2S3@BiYWO6 heterojunction photocatalysts for highly efficient environmental remediation

Novel In2S3@BiYWO6 heterojunction photocatalysts were designed and synthesized by a simple two-step hydrothermal method, which exhibit extremely excellent photocatalytic activity for degrading the residual antibiotics in wastewater. Especially, In2S3@BiYWO6 composite with mass ratio of 10:1 shows the highest photo-degradation efficiency towards Tetracycline Hydrochloride, which is about 2.46 and 7.55 times than that of pristine In2S3 and BiYWO6, respectively. A direct Z-scheme charge transfer mechanism was demonstrated in these heterojunctions through the XPS analysis, radical species trapping experiments and fluorescence detection. Within the framework of this mechanism, the critical built-in electric field (Ei) formed at the contact interface between In2S3 and BiYWO6 spatially separates reduction or oxidation sites and thus preserves the photogenerated carriers with stronger redox ability on reaction sites, which ultimately enhances the photocatalytic activity of the heterojunction catalysts. It is commendable that such Z-scheme heterostructures between In2S3 and BiYWO6 exist in a wide span of component ratios (from 5:1 to 30:1), which is beneficial for the environmental remediation applications. It is believed that this work provides new ideas for design and synthesis of novel Z-scheme heterojunction photocatalysts.

Construction of ZnCdS/TiO2 Z-Scheme heterostructure with excellent photocatalytic performance for degradation of norfloxacin

In this study, the binary heterojunction photocatalyst of ZnCdS modified TiO2 nanorod arrays was successfully prepared by hydrothermal method and successive ionic layer adsorption and reaction (SILAR). The ZCST-12 showed high removal efficiency (93.1%) of norfloxacin (NOR) within 90 min. The rate constant Kα was 0.0278 min−1 and the transient photocurrent density of ZCST-12 was up to 63 μA/cm2, which were 3.08 and 3.7 times higher than that of unmodified TiO2. The synergistic effect of ZnCdS and TiO2 broadens the range of light absorption, makes the absorption edge red shift, and greatly improves the light absorption and utilization ability of the material. The ZnCdS/TiO2 Z-scheme heterojunction greatly promotes the separation of electrons and holes and accelerates the carriers transport, preserves the strong redox ability of spatially separated holes and electrons, and effectively improves the photocatalytic performance. This study provides a simple method for preparing ZnCdS/TiO2 heterojunction photocatalyst.

Decorating Thermodynamically Stable (101) Facets of TiO2 with MoO3 for Multifunctional Sustainable Hydrogen Energy and Ammonia Gas Sensing Applications.

The simultaneous realization of sustainable energy and gas sensors dealing with the emission of pollutants is indispensable as the former thrives on the minimization of the latter. However, there is a dearth of multifunctional nanocatalysts in the literature. This ascertains the importance of multifunctional semiconductors which can be utilized in H2 generation via overall water splitting and in the gas sensing of global pollutants such as NH3. MoO3-decorated TiO2 Z-scheme heterostructures exceptionally escalate the photochemical and photo/electrochemical H2 evolution performance and gas sensing response of TiO2 owing to the synergistic relationship between TiO2 and MoO3. Extensive structural, morphological, and optical characterizations, theoretical studies, and XPS results were exploited to develop a mechanistic framework of photochemical H2 evolution. The photochemical response of the optimum TiO2-MoO3 composition (20 wt % MoO3-TiO2) was found to be nearly 12- and 20-fold superior to the pristine TiO2 and MoO3 photocatalysts, respectively, with the remarkable H2 evolution rate of 9.18 mmol/g/h and AQY of 36.02%. In addition, 20 wt % MoO3-TiO2 also showed advanced photo/electrochemical efficiency with 0.61/0.7 V overpotential values toward HER due to the higher electrochemically active surface area and Tafel slope as low as 65 mV/dec. The gas sensing response of 20 wt % MoO3-TiO2 toward NH3 gas turned out to be 2.5-fold higher than that of the pristine TiO2 gas sensor.

All-solid-state Z-scheme nanojunction PW12/Ag/ZnO photocatalyst: Effective carriers transfer promotion and enhanced visible light driven

By coupling two semiconductors with favorable band gap, ZnO (PS I) and Keggin-type tungstophosphate (PW12, PS II), an interesting all-solid-state Z-scheme photocatalyst PW12/Ag/ZnO has been designed and synthesized. In the developed composite PW12/Ag/ZnO, noble metal silver nanoparticle as an efficient conductor constructs an efficient spatial charge separation and carriers transfer process. By controlling reaction conditions, the UV–Vis absorption of Ag nanoparticles in the designed all-solid-state Z-scheme complex is gradually improved from about 400 nm to near infrared region. Benefited from its effective visible light absorption, the developed photocatlyst exhibits favorable UV-visible response, enhanced photocatalytic performance with optimum photodegradation of PW12/Ag-4/ZnO-6 for model dye (RhB ca. 99.93% at pH=6) and high reaction kinetics. Results show that the migration pathway of the charge carriers in this ternary system is significantly altered in counterparts of binary catalysts PW12/Ag and PW12/ZnO. The synergy catalysis interaction occurs between ·OH and ·O2− during the photodegradation process of PW12/Ag/ZnO composites. This work offers insights into the construction of efficient and stable all-solid-state Z-scheme heterostructures based on POMs.

Effective enhanced photocatalytic H2O2 production through synergistic oxygen vacancy defects and In situ-growth Z-scheme BiOBr/WO3 heterojunction with compact interface

Rational heterojunction interface construction and defect engineering have been regarded as significant strategies to enhance the photocatalytic performance of hydrogen peroxide (H2O2) production. Herein, a novel 2D/1D BiOBr/WO3 Z-scheme heterostructure with compact interface and rich oxygen vacancies (OVs) was successfully fabricated by an in situ-growth procedure. The rational design architecture and electronic structure allow the photocatalytic system to fully optimize light absorption, charge separation, and surface redox reaction. Benefited from synergistic effect of the formation of compact Z-scheme heterostructur and oxygen vacancies, the as-prepared BiOBr/WO3 photocatalysts exhibit a greatly improved photocatalytic performance in the production of H2O2 with a yield of 82.4 mM/h/g. We believe that this work provides a novel sight to develop high-efficiency photocatalyst via microstructure nanointerface control and defect engineering.

Oxygen-Independent Synchronized ROS Generation and Hypoxia Prodrug Activation with Z-Scheme Heterostructure Sonosensitizer.

Combination therapy has emerged as a promising approach for effective tumor treatment. However, the combination of sonodynamic therapy (SDT) and hypoxia-activated prodrugs (HAPs) has not been explored due to the contradictory requirement of oxygen (O2 ) for reactive oxygen species (ROS) generation and the necessity to avoid O2 for the activation of HAPs. In this study, this challenge is addressed by developing BiOCl-Au-Ag2 S Z-scheme heterostructure nanoparticles loaded with tirapazamine (TPZ) to achieve O2 -independent therapy. These nanoparticles demonstrate efficient electron-hole separation under ultrasound irradiation while maintaining a high redox potential. The generated holes react with water to efficiently produce hydroxyl radicals, while the electrons autonomously activate TPZ, negating the need for O2 . In vitro and in vivo assessments validate the effective tumor elimination by these Z-scheme nanoparticles without disrupting the hypoxic environment. This innovative design overcomes the limitations associated with O2 requirement in SDT and introduces a novel strategy for HAP activation and synergistic therapy between ROS and HAPs-based therapy.

Preparation of MgIn2S4/g-C3N4 for enhanced ranitidine photocatalytic degradation activity via Z-scheme electron transfer

The evidence so far indicates that ranitidine (RAN) contains N-nitrosodimethylamine (NDMA), a strong carcinogen, which is extremely harmful to human health under long-term exposure. Hence, a well-design Z-scheme heterostructure composed of 3D MgIn2S4 micro-flower and 2D g-C3N4 nanosheets was fabricated and used to remove RAN. The optimal photocatalyst (MG-30) exhibited the fastest RAN degradation rate of 0.24685 min−1 within 30 min under visible light, which was 78.1 and 19.8 times higher than those of bare MgIn2S4 and g-C3N4, respectively. Impressively, MG-30 was exceedingly resistant to environmental variations including organic matter, inorganic salts and aqueous substrates. In the meantime, MG-30 boasted the merit such as wide pH range for RAN removal. The excellent results originated from the construction of Z-scheme heterojunctions, which improved the carrier separation efficiency and retained the strong redox ability of MG-30, thereby contributing to the creation of rich active species. Meanwhile, the 3D/2D structure of MgIn2S4/g-C3N4 overrode the limited reflection of visible light. The active species analyses revealed that superoxide radical (·O2−) and hydroxyl radical (·OH) mainly participated in RAN degradation. Furthermore, the possible degradation pathways of RAN and toxicity analysis of intermediates produced were presented. This work emphasizes practical application potential of Z-scheme heterostructure photocatalysts for emerging contaminants degradation in wastewater.

MOF-Derived In2O3 Microrod-Decorated MgIn2S4 Nanosheets: Z-Scheme Heterojunction for Efficient Photocatalytic Degradation of Tetracycline.

The construction of Z-scheme heterostructures using matching band semiconductors is an effective strategy for producing highly efficient photocatalysts. In this study, MgIn2S4(MIS) was grown in situ on In2O3 microrods created with an In-based MOF material (In-MIL-68) as a template to successfully establish a unique MIS-In2O3 heterojunction with a well-matched Z-scheme interface charge transfer channel. Tetracycline (TC) as a typical antibiotic was chosen as the target pollutant to evaluate the photocatalytic activity. After 120 min of visible light irradiation, the MIS-In2O3-(10:1) material had the greatest photocatalytic degradation activity of tetracycline with 96.55%, which was 2.39 and 4.26 times that of MIS and In2O3, respectively. The improved photocatalytic activity is attributed to the in situ growth of MIS on In2O3, forming a Z-scheme heterojunction at the interface, which not only increases the specific surface area, exposes the abundant active site, and improves light utilization but also facilitates the migration and separation of photogenic carriers. The photocatalytic degradation products of TC were detected by liquid chromatography-mass spectrometry (LC-MS), and a preliminary degradation pathway was proposed. Radical capture experiments and ESR analysis confirmed that the main active species were holes (h+), superoxide radicals (•O2-), and superoxide and hydroxyl radicals (•OH). Finally, combined with band position analysis, this study proposes a direct Z-scheme heterojunction mechanism to improve the photocatalytic degradation of tetracycline in MIS under visible light.

Z-Scheme Heterostructures Using Band-Gap-Tunable ZnO by Metal Doping and Coupling with Polypyrrole for Enhanced Photocatalytic Water Splitting

Z-Scheme Heterostructures Using Band-Gap-Tunable ZnO by Metal Doping and Coupling with Polypyrrole for Enhanced Photocatalytic Water Splitting

Direct Z-scheme MoSTe/g-GeC heterostructure for photocatalytic water splitting: A first-principles study

In this paper, based on the first-principle calculations of hybrid density functional theory, the MoSTe/g-GeC of the Z-scheme heterostructure is constructed. The stability, electronic properties, optical absorption properties, and photocatalytic mechanism of the heterostructure is investigated. The band structure of MoSTe/g-GeC heterostructure is staggered, and the bandgap is 0.47 eV. The built-in electric field from g-GeC to MoSTe, with a size of 1.03 eV. The optical absorption coefficient of MoSTe/g-GeC heterostructures is significantly higher than that of MoSTe and g-GeC layer. When pH ranges from 0 to 7, the reduction reaction occurs in g-GeC layer, and the oxidation reaction occurs in the MoSTe layer. In the MoSTe/g-GeC heterostructure under different stresses, the band structure is arranged in a staggered manner. Importantly, under tensile strain, the bandgap of MoSTe/g-GeC heterostructure can be changed from the indirect into a direct bandgap. The bandgap of heterostructure decreases under the strain. In addition, the analysis of the photocatalytic mechanism shows that the redox reaction of the MoSTe/g-GeC heterostructure occurs on the layer with strong redox ability, and their light absorption ability is significantly enhanced compared to single-layers, which effectively improves the photocatalytic properties. It's a potential high-efficiency photocatalytic materials for direct Z-scheme heterostructure.

Visible light photocatalytic degradation of dyes by Ag3PO4/g-C3N4/CQDs composite

To facilitate the realize high-value utilization of coal tar pitch, carbon quantum dots (CQDs) were synthesized using ball-milling-assisted H₂O₂ oxidation method with tar pitch as carbon source. Subsequently, Ag₃PO₄/g-C₃N₄/CQDs composites were prepared through the electrostatic self-attraction of CQDs, Ag₃PO₄ and g-C₃N₄. These composites were then employed for the photocatalytic degradation of dyes, including methyl orange (MO), methylene blue (MB) and rhodamine B (RhB). A case study of MO, the degradation rate constant of Ag₃PO₄/g-C₃N₄/CQDs reached 0.02469 min−1, which was 11 times and 1.6 times higher than that of g-C₃N₄ and Ag₃PO₄. It found that Ag₃PO₄:g-C₃N₄ mass ratio of 1:1 and 5 mg/L CQDs solution loading were optimal. Characterization analysis revealed the specific surface area of the catalyst was increased and optimized band gap structure after the combination of CQDs as the co-catalyst. The possible reaction mechanism was also expounded, Ag₃PO₄/g-C₃N₄/CQDs constructed Z-scheme heterostructure, with CQDs as electron bridge. In addition, the impact of catalyst mass, initial concentration, and pH on the degradation process was studied, as well as the cyclic stability of the catalyst. Based on capture and ESR tests, the main active substances involved in the reaction were in the following order: h+ > ·OH > ·O2−. These experiments provided a new idea on the application of coal-based CQDs in the field of visible light catalytic degradation.

MOF-derived C, N-In2O3 with GdFeO3 Z-scheme heterostructure for the photocatalytic removal of tetracycline

Metal oxides derived from metal–organic frameworks have received considerable attention for water treatment. Herein, MIL-68 (In)–derived rod-like carbon (C) and nitrogen (N) codoped In2O3–modified GdFeO3 (CN–InO/GdF) Z-scheme heterostructures were rationally constructed through simple pyrolysis and a wet-chemical route. The synthesized CN–InO/GdF catalysts were characterized using several physicochemical techniques. Moreover, the obtained CN–InO/GdF exhibited excellent photocatalytic performance toward tetracycline (TC) degradation. Impressively, the optimized CN–InO/GdF-3 heterostructure catalyst displayed a boosted TC removal efficiency of 99.06% within 60 min of irradiation, which was 7.1 and 9.7 times higher than those of bare CN–InO and GdFeO3, respectively. The remarkably enhanced photoactivity of CN–InO/GdF was principally attributed to the synergistically combined interfaces hindering the recombination of photoinduced carriers, and the maintained redox capacity via Z-scheme spatial charge transfer. Finally, the tentative degradation mechanism was determined on the basis of density functional theory calculations and intermediates analysis. This work elucidated the design of highly efficient catalysts for various applications.

Highly stable lead-free perovskite Cs2AgBiBr6/UiO-66 Z-scheme heterostructures with enhanced photocatalytic activity for CO2 photoreduction and organic dyes degradation

Excessive combustion of traditional fossil fuels causes seriously global warming (Carbon dioxide, CO2) and energy crisis. Photocatalytic CO2 conversion to fuels has emerged as one of the most effective strategies. Herein, an environmentally friendly nanocomposite based on lead-free Cs2AgBiBr6 (CABB) perovskite nanocrystals and the UiO-66 metal–organic framework was fabricated by a facile ultrasonic process for efficient CO2 photoreduction. The obtained CABB/UiO-66 consisted of uniform CABB nanocrystals (10–12 nm) attached to the UiO-66 surface and exhibited a high surface area (1031 m2/g). The composite displayed enhanced light-harvesting capacity than the individual components and provided sufficient active sites for promoting photocatalytic activity. A typical Z-scheme heterostructure between the CABB and UiO-66 was realized by forming an inner electric field, leading to the occurrence of efficient excited state charge transfer. The efficient charge transfer of CABB/UiO-66 inspired its use as an active photocatalyst for the reduction of CO2 with significantly improved photocatalytic activity against its individual components. Specifically, CABB/UiO-66 exhibited 38 and 40-fold improvement in catalytic activity compared to respective CABB and UiO-66 in terms of the total yield of CO, CH4, and C2H6. Moreover, the nanocomposite displayed excellent activity towards the oxidative photocatalytic degradation of aqueous environmental contaminant rhodamine B. We believe that this work provides a guide for designing lead-free perovskite-based renewable catalysts and offers new opportunities for the photocatalytic conversion of CO2 photoreduction.